This disclosure relates to a rotary expander for a waste heat recovery system, and in particular, to a sliding vane rotary expander.
Fuel economy can be improved for internal combustion engines by utilizing a waste heat recovery system. One type of waste heat recovery system utilizes a Rankin cycle loop where a working fluid receives heat rejected by an EGR cooler. The recovered waste heat is converted into useful work through an expander and compounded with the engine output through a compounding device, such as an alternator. Typically, the expander greatly influences the overall efficiency of the waste heat recovery system, the power compounding method and system cost.
One type of expander is a rotary expander, which includes sliding vane expanders. The performance of sliding vane expander is typically not very good due to a low pressure expansion ratio relating to its low volumetric efficiency resulting from internal leakage. Increasing rotational speed of a sliding vane expander improves the volumetric efficiency, however, the siding friction of the vanes against its housing also increases leading to deterioration in the mechanical efficiency of the expander.